Electric power may be produced using poly-phase electric machines, also referred to as motor/generators. Synchronous electric machines may operate at constant speeds and frequencies under steady-state conditions. Synchronous electric machines, e.g., permanent magnet (PM) motors, operate via the principal of electromagnetic induction, with an electromotive force (EMF) generated via an induced flux by relative motion of conductive coils or windings. A synchronous electric machine typically includes a magnetic field structure and an armature. The armature may have a three-phase load winding, which in turn generates an alternating current (AC) EMF. In particular, a stationary or stator portion of a three-phase synchronous electric machine carries the armature winding, which carries a three-phase excitation.
Induction machines are another type of poly-phase electric machine that are also widely used for electric power generation. Like the synchronous electric machine described above, the induction machine or motor includes a stator and rotor, with the stator having a cylindrical core portion carrying windings or coils within its slots. AC is supplied to the stator windings, and a current is thus inducted in the windings of an opposing cylindrical rotor, with the opposing fields acting to rotate the rotor.
Regardless of whether they are used in synchronous-type or in induction-type electric machines, motor phase windings may have minor manufacturing defects between turns or slots, or may develop such defects over time. The defects, although minor, may cause a phase imbalance. A motor controller may perform a stable operation with such defects being present in the phase windings without experiencing any unduly degraded performance. However, over an extended period any incipient defects in the phase windings can lead to a breakdown in the surrounding winding insulation material, which may ultimately lead to other defects or performance issues, such as open and/or shorted phase windings.